Usually, in the processing of plastics material spectacle lenses a spectacle lens blank, commonly referred to only as a “blank”, is provided which has a standardized, finished convex outer surface with, for example, a spherical or progressive shape and which is molded from plastics material (for example polycarbonate, CR 39, HI-Index, etc.). The inner or prescription surfaces, which are usually concave, are machined to provide a spherical, aspherical, toroidal, atoroidal, progressive or freely shaped geometry (varifocal surface) depending on the respectively desired optical effect. The typical conventional sequence for inner surface processing provides, after blocking of the spectacle lens blank by its outer surface on a block member, optionally a processing by milling and, particularly, turning for production of the optically active shape, usually followed by a fine grinding or polishing process for attainment of the necessary surface quality.
In the prior art, use is also made for the above-mentioned turning process of so-called fast-tool lathes in which a lathe chisel can be moved highly dynamically either in linear reciprocation (See, for example, specification WO-A-02/06005) or in rotation (See for example, specification WO-A-99/33611) so that lens surfaces which are not rotationally symmetrical or are ‘non-round’ can be produced in the turning process. The actual turning, i.e. the cutting process, in that case is carried out with supply of a liquid cooling lubricant to the cutting edge of the lathe tool. On the one hand the cooling lubricant has to cool and lubricate at the cutting location so as to prolong the service life of the lathe tool and to assist the advance and on the other hand the cooling lubricant has to ensure optimum removal of chips and in that case also bind fine material particles, which have arisen during the cutting and which in the case of dry processing would, due to their size, pass as dust and possibly place the health of the user at risk.
In the prior art, a liquid cooling lubricant is commonly supplied to the cutting edge of the lathe tool at a fast-tool lathe through segmented hose systems for example the Loc-Line® Flexi System of Lockwood Products, Inc., Lake Oswego, Oreg., USA (cf. specification EP-A-0 167 063); see, for example, the brochure, “VFT-compact-pro” of Satisloh AG, Baar, Switzerland on page 1 (small illustration: orange-colored segmented hose above the lathe chisel). These segmented hoses have individual specially shaped, stiff plastics material segments, of which several are plugged together to form a segmented hose of predetermined length. Because of the stiffness, ‘segment pipe’ would be a better term for these systems. The individual plastics material segments are then pivotably interconnected, yet with positional stability, so that the segmented hose can be oriented with respect to the lathe chisel. At the inlet end the segmented hose is coupled to a connection, which is stationary with respect to a housing of the fast-tool servo and which can be supplied with the cooling lubricant from a cooling lubricant source. At the outlet end the segment hose is usually provided with a nozzle segment forming an outlet, which is in fluid connection by way of the segmented hose with the connection at the housing side, for delivery of a cooling lubricant jet to the lathe chisel.
These segmented hoses are indeed simple to align, by a grip, to any desired position, in which they also remain with a high degree of vibration insensitivity and positional stability. However, the cutting edge of the lathe chisel driven by way of the fast-tool servo moves highly dynamically, in the case of turning of non-round lens surfaces over a total stroke of at most approximately 30 millimeters, for example oscillating at up to 200 Hz or more, over a processing stroke of at most approximately 10 to 12 millimeters below the cooling lubricant jet delivered by the stationary segmented hose, so that the cooling lubricant jet is not always directed in the best possible manner onto the location of the cutting. Different thicknesses and curvatures of the spectacle lens to be processed additionally require a re-arrangement of the segmented hose system or a widely fanned cooling lubricant jet, which for the most part does not impinge on the point of action of the lathe chisel.
What is needed is a device of simplest possible construction for the feed of liquid cooling lubricant to a cutting edge of a lathe tool drivable in oscillation by a fast-tool servo, which device reliably ensures that the cooling lubricant always reaches, in the best possible way, the location of the cutting.